1. Field of the Invention
The present invention relates to a flat cable high-frequency filter and a flat cable high-frequency diplexer, each of which is a thin, flat film and has a frequency selection function, and an electronic device including the flat cable high-frequency filter or the flat cable high-frequency diplexer.
2. Description of the Related Art
Hitherto, an electronic device using high-frequency signals, such as a mobile terminal, includes a high-frequency filter for separating a high-frequency signal in a desired frequency band from unwanted high-frequency signals and harmonic signals.
The structure of a known high-frequency filter is, for example, the structure disclosed in Japanese Unexamined Patent Application Publication No. 2002-57543. The high-frequency filter disclosed in this publication is constituted by a mounting multilayer body obtained by stacking a plurality of dielectric layers and by sintering them. Inductors and capacitors forming the high-frequency filter are implemented by conductor patterns formed within the multilayer body.
In accordance with a reduced size of an electronic device, the mount area for a high-frequency filter constituted by the above-described mounting multilayer body is more and more restricted. It is thus demanded that the size of a high-frequency filter be also reduced. In this case, the size and the thickness of conductor patterns formed within the multilayer body forming inductors and capacitors are also decreased.
However, if the size of a mounting high-frequency filter is reduced, the device characteristics of inductors and capacitors are decreased. For example, concerning inductors, the equivalent series resistance (ESR) is increased due to a decrease in the thickness of the inductors. Concerning capacitors, the equivalent series inductance (ESL) is increased due to a complicated wiring pattern for forming a high-frequency filter. Because of the decreased device characteristics, the Q factor of the high-frequency filter is reduced, thus increasing the loss in the high-frequency filter.
When connecting a high-frequency filter between circuits on a plurality of mount boards, one of the following structures is employed for the above-described known mounting high-frequency filter. The high-frequency filter is mounted on one mount board and is connected to the other mount board by using a flat cable. Alternatively, an intermediate mount board is disposed between two mount boards, and a high-frequency filter is mounted on this intermediate mount board and is connected to the two mount boards by using flat cables.
With the above-described structures, transmission loss occurs in the individual flat cables, and thus, in addition to the loss in the above-described high-frequency filter, transmission loss is also incurred.
A mounting multilayer body forming a high-frequency filter requires a certain height. Accordingly, a space is required on the mount surface of a mount board in accordance with the height of the multilayer body.